Multistage turbocompressor

ABSTRACT

A multistage turbocompressor is provided for compressing a process gas. The turbocompressor has includes a rotor and a casing. A gas seal is associated in each case with a first turbocompressor stage and a last turbocompressor stage for sealing a penetration of a rotor shaft through a wall of the at least one casing, against a respective stage inlet pressure or stage discharge pressure. The gas seals are connected to a sealing gas line via which they are supplied with a sealing gas. A pressure chamber on a pressure side of the gas seal of the last stage which provides sealing against pressure discharge to the environment is connected to a relief line which opens into a pressure sink. A plurality of sealing gas lines are connected to a sealing gas feed line in which at least one control valve is arranged between junctions of different sealing gas lines.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the US National Stage of International Application No. PCT/EP2010/054576, filed Apr. 7, 2010 and claims the benefit thereof. The International Application claims the benefits of German application No. 10 2009 017 614.4 DE filed Apr. 16, 2009. All of the applications are incorporated by reference herein in their entirety.

FIELD OF INVENTION

The invention refers to a multistage turbocompressor, having at least one rotor and at least one casing, which compresses a process gas from an inlet pressure at the inlet of a first stage to a discharge pressure at the exit of a last stage, wherein at least one gas seal is associated in each case with at least the first and the last stages and externally seals the penetration of a rotor shaft through a wall of the casing, or casings, against a respective stage inlet pressure or stage discharge pressure, wherein the gas seals are connected to at least one sealing gas line by means of which it is supplied with sealing gas, wherein at least one pressure chamber on the pressure side of the gas seal of the last stage, which provides sealing against pressure discharge to the environment, is connected to at least one relief line which opens into a pressure sink.

BACKGROUND OF INVENTION

In the field of turbocompressors, gas seals, especially in a tandem arrangement, have the task of sealing shaft penetrations from the pressure chamber inside the casing in relation to the atmosphere. The gas seals are contactless seals and are lubricated with dry, filtered sealing gas. This sealing gas is normally extracted from the pressure connector of the last stage, which has the highest pressure. After this, it is filtered, possibly heated, and via orifice plates or throttle valves is reduced in pressure and directed to the individual gas seals by means of supply lines. Since the stages from the first to the last stage are steadily increasing in pressure, different differential pressures are realized at the individual orifice plates or throttle valves. The stages are normally sealed against the discharge pressure downstream of its impeller. This means that the orifice plate or the throttle valve in the feed line of the sealing gas to the gas seal, which is associated with the first process stage, a high pressure difference is reduced, whereas the orifice plate in the sealing gas feed line to the gas seal of the last stage of the turbocompressor has to reduce only a very low pressure difference. Consequently, the opening cross section of the throttle valve or the orifice plate diameter at the first stage is relatively small and proportionally large at the last stage in order to provide the necessary quantity of sealing gas there.

If the turbocompressor within its operating map is run at the absorption limit, it requires a high volume with only a low pressure build up. In this case, the differential pressure between the pressure in the pressure connector and the discharge pressure downstream of the impeller of the last process stage (possibly depending upon the process of the last two stages) is low in such a way that a sufficient sealing gas supply via the existing orifice plates or throttle valve settings is no longer possible. In this case, unfiltered, potentially moist process gas can get to the gas seal and damage this.

A turbocompressor of the type referred to in the introduction is already known from DE 24 11 243 A1; U.S. Pat. No. 3,795,460 A and JP 2000073990 also show turbocompressors with sealing gas supplies.

SUMMARY OF INVENTION

Based on the previously described problems of the prior art, the invention is based on the object of creating improved sealing of multistage turbocompressors, which prevents the gas seals being exposed to the action of unfiltered process gas.

For achieving the object according to the invention, a turbocompressor according to the independent claim is proposed.

The relieving according to the invention of the pressure chamber on the pressure side of the gas seal ensures the necessary pressure difference in order to ensure the sealing effect or to ensure an inflow of sealing gas for the supply of the gas seal through the sealing gas line, especially in operating states which are characterized by an only low pressure build up in the multistage turbocompressor. The relief line is preferably dimensioned in such a way that the achieved pressure drop in the pressure chamber on the pressure side of the gas seal is sufficient for adequate sealing gas to flow in and for no process gas to find its way to the gas seal. Furthermore, the dimensioning be such that no more sealing gas is consumed than is necessary for achieving the sealing effect and for reliable operation. A discharge into a stage of the turbocompressor where a lower pressure exists than in the pressure chamber is preferably as a pressure sink. The discharge into an inlet into a stage is especially expedient in this case. In this way, the process gas is circulated at an only low rate for the purpose of the intended pressure relief. In order to minimize as far as possible the consumption of pre-pressurized process gas or to minimize the portion of process gas which is expanded as a result of the pressure relief, it is expedient if an additional shaft seal is provided between the pressure chamber and a stage exit of the associated stage. This is preferably designed as a labyrinth seal. This additional shaft seal can bring about a necessary pressure loss which is required so that the sealing gas, if it is tapped from the highest-pressure stage, has the pressure difference so that it flows into the gas seal.

Since many operating states do not create sufficient pressure difference (pre-pressurized when stationary, for example), it is advisable if a foreign gas, that is to say a gas which does not originate directly from the path of the process gas through this turbocompressor, is made available as sealing gas for this.

An especially preferred field of application of the invention are turbocompressors in which a plurality of stages have at least one gas seal in each case, especially where a plurality of stages are provided in different casings which have in each case a gas seal at a penetration of the shaft through a casing wall. For minimizing the sealing gas consumption, it is also expedient if the sealing gas line, which is connected in each case to the gas seal, has a throttle valve or an adjustable valve by means of which the sealing gas pressure which is present at the seal during normal operation is set in such a way that the gas seal can properly fulfill its function and the consumption of sealing gas is minimized at the same time. A certain pressure reserve should be made available in this case in order to be able to pass through anticipated fluctuations of the operating state in an error-free manner.

The sealing gas lines of the individual gas seals are advantageously connected to a sealing gas feed line or to a sealing gas header. Between the individual junctions of the sealing gas lines, this sealing gas feed line can be provided with control valves which, in dependence upon the operating state, lowers the pressure in the downstream sealing gas lines. In this way, in addition to the static throttle in the sealing gas line, there is preferably an adjustability of the sealing gas feed, which in certain operating states counteracts an excessive consumption of sealing gas. On the other hand, this use of control valves enables the provision of a reserve which in case of need ensures the operational reliability of the gas seals. In particular, in combination with the relief lines according to the invention, the sealing gas consumption can thus be minimized on the one hand and on the other hand the operational reliability of the gas seals can be increased.

A valve which opens in case of need can be especially advantageously provided in the relief lines. This valve can be designed with a binary positioning option or can be gradually adjustable as a control valve, which second option additionally offers the opportunity—in the case of a relief requirement—to adapt the extent of the pressure relief to the actual requirement and at the same time not to excessively impair the efficiency of the overall arrangement.

A preferred central control unit can expediently control both the position of the control valves in the sealing gas feed line and that of the valves in the relief line, especially in dependence upon the volumetric flow in the sealing gas line. For this purpose, it is advisable to directly or indirectly measure the volumetric flow in the sealing gas lines. Reliable measuring can be carried out by means of a measuring arrangement at the throttles or adjustable valves in the sealing gas lines, which can deter mine the pressure difference there, which can allow a clear conclusion to be drawn about the volumetric flow. The control unit opens the control valve, or control valves, in the sealing gas feed line if the measurement for the volumetric flow through the sealing gas line of at least one gas seal falls below a first volumetric-flow limit value. Furthermore, the control unit opens the valves in the relief lines collectively or individually if an excessively low volumetric flow is determined at the respective measuring point in the sealing gas line, or an excessively low volumetric flow is determined at least one measuring point in a sealing gas line.

So that the control units for the control valves in the sealing gas feed line and for the valves in the relief lines are not mutually influenced, it is expedient if the setpoint values—which are to be adjusted—for the pressure difference across the orifice plates or the measurement for the volumetric flow have a minimum interval in relation to each other with regard to the operation of the control valves and of the valves. First of all, the control valves preferably open to the full opening extent in steps when approaching a first volumetric-flow limit value, and with a further drop in the volumetric flow, the relief valves open to the full opening extent in order to thus ensure the operational reliability of the gas seals.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is explained in the following text based on a particular exemplary embodiment with reference to a drawing. The invention is not limited to the particular development of this example, but rather further development possibilities of the invention are particularly—and in consideration of each possible combination of the patent claims—revealed to the person skilled in the art.

In the drawing:

FIG. 1 shows a schematic view of the multistage turbocompressor according to the invention.

DETAILED DESCRIPTION OF INVENTION

FIG. 1 shows a multistage turbocompressor TC which comprises six stages ST1 to ST6. Process gas PG enters each stage ST1 to ST6 and is compressed there from an inlet pressure p1 to p6 to a respective discharge pressure p2 to p7. The individual stages ST1 to ST6 have in each case a rotor R, upon which is arranged an impeller of a stage ST1 to ST6 which is designed as a radial compressor in each case. The stages are enclosed in each case by a casing C, through the casing wall of which the shaft of the rotor R is guided for the purpose of connecting to the drive, which is not shown in more detail. In the region of the penetration, provision is made for a gas seal DGS1 to DGS6 which seals the respective stage discharge pressure p2 to p7 in relation to the environment. The gas seal DGS1 to DGS6 is designed in each case as a dry gas seal and is supplied with a sealing gas SG by means of a sealing gas line SGL1 to SGL6. The gas seals DGS1 to DGS6 are provided in each case in a tandem arrangement, wherein a labyrinth seal LS is additionally provided in each case on the pressure side, between the two individual seals of the tandem arrangement of the gas seal DGS1 to DGS6, and on the environment side.

The two seal elements of the gas seals DGS1 to DGS6 have in each case a sealing plane which is not shown in detail and extends in the radial direction. The sealing gas is extracted from the exit EX at the last stage ST6 and after passing through a filter F1 and a heater HAT is introduced into a sealing gas feed line SGC. The sealing gas feed line SGC feeds the treated sealing gas SG into the associated sealing gas lines SGL1 to SGL6 for the supply to the gas seals DGS1 to DGS6. The sealing gas lines SGL1 to SGL6 are provided with individual throttles TH1 to TH6 which provide a sealing gas pressure which is adjusted to the respective pressure of the stage ST1 to ST6 in the region of the gas seal DGS1 to DGS6. The last stage ST6 has a separate pressure chamber PR upstream of the gas seal DGS6 which is isolated from the stage discharge pressure p7 by an additional rotor seal ARS which is designed as a labyrinth seal LS. The differential pressure which is reduced in the additional shaft seal ARS can be increased by opening a valve CV2 in a relief line RL which connects the pressure chamber PR to a pressure sink, in this case to the inlet into the stage ST6 at the pressure p6 of the inlet which lies below the pressure p7 of the exit EX.

The section of the junction of the sealing gas lines SGL4 to SGL6, which are associated with the fourth, fifth and sixth stage ST4 to ST6, is isolated from the remaining section of the sealing gas feed line SGC by means of a control valve CV12. A further control valve CV11 isolates the sealing gas lines SGL1 to SGL3 for the first, second and third stages ST1 to ST3 from the sealing gas feed line SGC. The two control valves CV11, CV12 in the sealing gas feed line SGC enable a requirement-based reduction in the pressure upstream of the throttles TH1 to TH6 of the first, second and third stages ST1 to ST3 or of the fourth, fifth and sixth stages ST4 to ST6 in conformance with different operating states. The stage ST3, ST6 with the highest pressure in each case in the section of the sealing gas feed line SGC which is controlled by the respective control valve CV11, CV12 is influential for controlling the position of the control valve CV11, CV12. This is based on the knowledge that so long as a sufficient volumetric flow flows through the orifice plate TH6 of the last stage ST6, especially the gas seals DGS4 and DGS5 of the fourth and fifth stages ST4, ST5 are adequately supplied with sealing gas SG. Correspondingly, this knowledge also forms the basis for the controlling of the control valve CV11 for the first, second and third stages ST1 to ST3. A measurement of the differential pressure pdt1, pdt2 of a third stage and of a sixth stage across the throttle TH3, TH6 there in the sealing gas line SGL3, SGL6 is transmitted to a control unit CR as a measurement for the volumetric flow there. This control unit CR controls the control valves CV11, CV12 in such a way that a first volumetric-flow limit value VL1, VL2 is not fallen short of in each case. If the pressure reserve in the sealing gas feed line SGC should not allow an additional increase in the pressure of the sealing gas SG downstream of the control valves CV11, CV12, the control unit CR additionally opens the valve CV2 in order to relieve the pressure chamber PR on the pressure side of the gas seal DGS6 of the last stage ST6 by means of the relief line RL. The thereby falling pressure ensures that through the sealing gas line SGL6 of the last stage ST6 or of the gas seal DGS6 there is adequate and a corresponding pressure difference is again established in the throttle TH6 there. For the comparatively low pressure level of the remaining stages ST1 to ST5, such a relief line RL is not necessary because the pressure level of the exit EX from the last stage ST6 is always higher.

For supply with a foreign gas FSG—that is to say a gas which does not directly originate from the path of the process gas through this turbocompressor—as sealing gas in specific operating states in which no adequate pressure difference prevails in the turbocompressor TC (for example when pressurized in the stationary state), a feed line into the sealing gas line SGC is provided. 

1-8. (canceled)
 9. A multistage turbocompressor for compressing a process gas from an inlet pressure at an inlet of a first stage of the turbocompressor to a discharge pressure at an exit of a last stage of the turbocompressor, the turbocompressor comprising: at least one rotor having a rotor shaft; at least one casing; at least one gas seal associated in each case with at least the first stage and the last stage for sealing a penetration of the rotor shaft through a wall of the at least one casing, against a respective stage inlet pressure or stage discharge pressure, wherein the gas seals are connected to at least one sealing gas line via which they are supplied with a sealing gas; wherein at least one pressure chamber on a pressure side of the at least one gas seal of the last stage which provides sealing against pressure discharge to the environment is connected to at least one relief line which opens into a pressure sink, and wherein a plurality of sealing gas lines are connected to a sealing gas feed line in which at least one control valve is arranged between junctions of different sealing gas lines.
 10. The turbocompressor as claimed in claim 9, wherein the pressure sink is a discharge into a stage of the turbocompressor where a lower pressure exists, or into an inlet into a stage.
 11. The turbocompressor as claimed in claim 9, wherein an additional shaft seal is provided between the pressure chamber and a stage exit of the associated stage.
 12. The turbocompressor as claimed in claim 9, wherein a gas seal is provided at a plurality of stages and the respectively associated sealing gas line has a respective throttle which adjusts the sealing gas pressure to the sealing pressure.
 13. The turbocompressor as claimed in claim 12, wherein the control valve is arranged upstream of the sealing gas line, and wherein a provision is made for a control unit which is designed in such a way that when a first volumetric-flow limit value is fallen short of as a result of the respective throttle, the control valve opens.
 14. The turbocompressor as claimed in claim 9, wherein provision is made in the relief line for a control valve which is controlled by a control unit, the control unit being designed in such a way that the control valve opens if a second volumetric-flow limit value is fallen short of.
 15. The turbocompressor as claimed in claim 14, wherein the control unit is designed in such a way that the first volumetric-flow limit value is lower than the second volumetric-flow limit value.
 16. The turbocompressor as claimed in claim 9, wherein provision is made for a measuring device which determines differential pressure across the throttle and transmits the same to the control unit as a measurement for the volumetric flow. 